4,554 research outputs found
Stretched exponential relaxation in a diffusive lattice model
We studied the single dimer dynamics in a lattice diffusive model as a
function of particle density in the high densification regime. The mean square
displacement is found to be subdiffusive both in one and two dimensions. The
spatial dependence of the self part of the van Hove correlation function
displays as function of a single peak and signals a dramatic slow down of
the system for high density. The self intermediate scattering function is
fitted to the Kohlrausch-Williams-Watts law. The exponent extracted
from the fits is density independent while the relaxation time follows a
scaling law with an exponent 2.5.Comment: 5 pages, 3 figures, to be published in Phys. Rev.
Deep GeMS/GSAOI near-infrared observations of N159W in the Large Magellanic Cloud
Aims. The formation and properties of star clusters at the edge of H II
regions are poorly known, partly due to limitations in angular resolution and
sensitivity, which become particularly critical when dealing with extragalactic
clusters. In this paper we study the stellar content and star-formation
processes in the young N159W region in the Large Magellanic Cloud.
Methods. We investigate the star-forming sites in N159W at unprecedented
spatial resolution using JHKs-band images obtained with the GeMS/GSAOI
instrument on the Gemini South telescope. The typical angular resolution of the
images is of 100 mas, with a limiting magnitude in H of 22 mag (90 percent
completeness). Photometry from our images is used to identify candidate young
stellar objects (YSOs) in N159W. We also determine the H-band luminosity
function of the star cluster at the centre of the H II region and use this to
estimate its initial mass function (IMF).
Results. We estimate an age of 2 + or - 1 Myr for the central cluster, with
its IMF described by a power-law with an index of gamma = - 1.05 + or - 0.2 ,
and with a total estimated mass of 1300 solar mass. We also identify 104
candidate YSOs, which are concentrated in clumps and subclusters of stars,
principally at the edges of the H II region. These clusters display signs of
recent and active star-formation such as ultra-compact H II regions, and
molecular outflows. This suggests that the YSOs are typically younger than the
central cluster, pointing to sequential star-formation in N159W, which has
probably been influenced by interactions with the expanding H II bubble
Incorporating climate change into invasive species management: insights from managers
Invasive alien species are likely to interact with climate change, thus necessitating management that proactively addresses both global changes. However, invasive species managers’ concerns about the effects of climate change, the degree to which they incorporate climate change into their management, and what stops them from doing so remain unknown. Therefore, we surveyed natural resource managers addressing invasive species across the U.S. about their priorities, concerns, and management strategies in a changing climate. Of the 211 managers we surveyed, most were very concerned about the influence of climate change on invasive species management, but their organizations were significantly less so. Managers reported that lack of funding and personnel limited their ability to effectively manage invasive species, while lack of information limited their consideration of climate change in decision-making. Additionally, managers prioritized research that identifies range-shifting invasive species and native communities resilient to invasions and climate change. Managers also reported that this information would be most effectively communicated through conversations, research summaries, and meetings/symposia. Despite the need for more information, 65% of managers incorporate climate change into their invasive species management through strategic planning, preventative management, changing treatment and control, and increasing education and outreach. These results show the potential for incorporating climate change into management, but also highlight a clear and pressing need for more targeted research, accessible science communication, and two-way dialogue between researchers and managers focused on invasive species and climate change
Stationary motion of a self gravitating toroidal incompressible liquid layer
We consider an incompressible fluid contained in a toroidal stratum which is
only subjected to Newtonian self-attraction. Under the assumption of
infinitesimal tickness of the stratum we show the existence of stationary
motions during which the stratum is approximatly a round torus (with radii r, R
and R>>r) that rotates around its axis and at the same time rolls on itself.
Therefore each particle of the stratum describes an helix-like trajectory
around the circumference of radius R that connects the centers of the cross
sections of the torus
A microscopic 2D lattice model of dimer granular compaction with friction
We study by Monte Carlo simulation the compaction dynamics of hard dimers in
2D under the action of gravity, subjected to vertical and horizontal shaking,
considering also the case in which a friction force acts for horizontal
displacements of the dimers. These forces are modeled by introducing effective
probabilities for all kinds of moves of the particles. We analyze the dynamics
for different values of the time during which the shaking is applied to
the system and for different intensities of the forces. It turns out that the
density evolution in time follows a stretched exponential behavior if is
not very large, while a power law tail develops for larger values of .
Moreover, in the absence of friction, a critical value exists which
signals the crossover between two different regimes: for the
asymptotic density scales with a power law of , while for
it reaches logarithmically a maximal saturation value. Such behavior smears out
when a finite friction force is present. In this situation the dynamics is
slower and lower asymptotic densities are attained. In particular, for
significant friction forces, the final density decreases linearly with the
friction coefficient. We also compare the frictionless single tap dynamics to
the sequential tapping dynamics, observing in the latter case an inverse
logarithmic behavior of the density evolution, as found in the experiments.Comment: 10 pages, 15 figures, to be published in Phys. Rev.
Coma revealed as an extended hard X-rays source by INTEGRAL IBIS/ISGRI
Aims. We report the INTEGRAL/IBIS observations of the Coma Cluster in the
hard X-ray/soft-ray domain. Methods. Since the Coma Cluster appears as an
extended source, its global intensity and significance cannot be directly
extracted with standard coded mask analysis. We used the method of imaging the
extended sources with a coded mask telescope developed by Renaud et al. (2006).
Results. The imaging capabilities and the sensitivity of the IBIS/ISGRI coded
mask instrument allows us to identify for the first time the site of the
emission above ~ 15 keV. We have studied the Coma Cluster morphology in the
18-30keV band and found that it follows the prediction based on X-ray
observations.We also bring constraints on the non-thermal mechanism
contribution at higher energies.Comment: 4 pages, 4 figures, Accepted for publication in A&A Letter
Coupling MOAO with Integral Field Spectroscopy: specifications for the VLT and the E-ELT
[Abridged] We have developed an end-to-end simulation to specify the science
requirements of a MOAO-fed integral field spectrograph on either an 8m or 42m
telescope. Our simulations re-scales observations of local galaxies or results
from numerical simulations of disk or interacting galaxies. For the current
analysis, we limit ourselves to a local disk galaxy which exhibits simple
rotation and a simulation of a merger. We have attempted to generalize our
results by introducing the simple concepts of "PSF contrast" which is the
amount of light polluting adjacent spectra which we find drives the smallest EE
at a given spatial scale. The choice of the spatial sampling is driven by the
"scale-coupling", i.e., the relationship between the IFU pixel scale and the
size of the features that need to be recovered by 3D spectroscopy in order to
understand the nature of the galaxy and its substructure. Because the dynamical
nature of galaxies are mostly reflected in their large-scale motions, a
relatively coarse spatial resolution is enough to distinguish between a
rotating disk and a major merger. Although we used a limited number of
morpho-kinematic cases, our simulations suggest that, on a 42m telescope, the
choice of an IFU pixel scale of 50-75 mas seems to be sufficient. Such a coarse
sampling has the benefit of lowering the exposure time to reach a specific
signal-to-noise as well as relaxing the performance of the MOAO system. On the
other hand, recovering the full 2D-kinematics of z~4 galaxies requires high
signal-to-noise and at least an EE of 34% in 150 mas (2 pixels of 75 mas).
Finally, we carried out a similar study at z=1.6 with a MOAO-fed spectrograph
for an 8m, and find that at least an EE of 30% at 0.25 arcsec spatial sampling
is required to understand the nature of disks and mergers.Comment: 17 pages, 20 figures, accepted for publication in the MNRA
Cytokine receptor expression in human lymphoid tissue: analysis by fluorescence microscopy
A highly-sensitive flourescence method, capable of detecting cytokine receptors present at low concentrations (around I DO molecules per cell) by flow cytometry, was adapted for use on tissue sections. This method was used to examine the expression of several cytokine receptors in lymphoid ti ss ues. lL-2 receptors were distributed broadly, with higher concentrations in T cell areas. lL-1 receptor Type I was detected in T cell areas and in the follicular mantle, and was strongly expressed on vasc ular endothelium. IL-6 receptor was found at very low concentration, both within and outside germinal centres. The gp 130 molecule, which is involved in the functional receptor complex for IL-6 and several other cytokines, was present at higher concentrations, particularly in the germinal centre. Analysis of receptor expression in secondary lymphoid tissue provides evidence bearing on the physiological roles of cytokines, as these tissues contain cells at various stages of physiological activation located in well-defined functional zones.Heddy Zola, Jodie Ridings, Helen Weedon, Michael Fusco, Roger W. Byard, Peter J. Macardl
A probable giant planet imaged in the Beta Pictoris disk
Since the discovery of its dusty disk in 1984, Beta Pictoris has become the
prototype of young early-type planetary systems, and there are now various
indications that a massive Jovian planet is orbiting the star at ~ 10 AU.
However, no planets have been detected around this star so far. Our goal was to
investigate the close environment of Beta Pic, searching for planetary
companion(s). Deep adaptive-optics L'-band images of Beta Pic were recorded
using the NaCo instrument at the Very Large Telescope. A faint point-like
signal is detected at a projected distance of ~ 8 AU from the star, within the
North-East side of the dust disk. Various tests were made to rule out with a
good confidence level possible instrumental or atmospheric artifacts. The
probability of a foreground or background contaminant is extremely low, based
in addition on the analysis of previous deep Hubble Space Telescope images. The
object L'=11.2 apparent magnitude would indicate a typical temperature of ~1500
K and a mass of ~ 8 Jovian masses. If confirmed, it could explain the main
morphological and dynamical peculiarities of the Beta Pic system. The present
detection is unique among A-stars by the proximity of the resolved planet to
its parent star. Its closeness and location inside the Beta Pic disk suggest a
formation process by core accretion or disk instabilities rather than a
binary-like formation process.Comment: 5 pages, 3 figures, 1 table. A&A Letters, in pres
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